Diamond Shape

Diamonds are available in various shapes, the more common shapes are shown below. All shapes have different types of facets which reflect the light. For example the round brilliant, cushions, radiant, oval, pear, marquise, heart and princess cut diamonds have small facets (underneath) giving them more sparkle where as the emerald, baguette and the asscher cut diamond facets are longer giving a more subtle sparkle.

The most popular is the round brilliant and has been for many years. As it has the highest demand the rounds are more expensive than other shapes. Also it has the most amount of waste when it is cut from the rough stone.

Shapes such as the baguettes and trilliants tend to be accent stones in a setting with one of the other shaped stones.

Diamond Carat Weight

Diamonds are weighed in carats not in grams. (A one carat diamond should weight 0.2grams). There are 100 points in one carat like there are 100 pennies in a GBP. The word carat originates from the carob seed which were often used as counterweights to balance scales many years ago. Precious and semi precious gemstones can also be measured in this way or by the mm size.

The most popular engagement ring carat sizes vary from 0.30ct up to 1.00ct and the price will increase the larger the diamond.

Diamond Colour

Colour grading is so subtle and can't always been seen to the untrained eye  but these slight difference do make a big difference to the value. The best colourless grade (D) is the whitest a diamond can be and the colour scale goes right down to a light yellow or brown (Z). The less colour the diamond has the higher it's value (except for fancy coloured diamonds). D, E and F are known as the 'collection colours' which are the ideal colours. 

The GIA (Gemological Institute of America) set the colour grading scale industry standard. 

At Avanti we will always recommend colours from D down to H/I. H/I are still near colourless but you can could see the slight colour difference if you the diamond next to a D colour.

As for fancy coloured diamonds these are graded in a much more complex way using hue, tone and saturation.

Diamond Clarity

Like colour the clarity of a diamond also uses a sliding scale. some companies use slightly different terminology but we will be using the GIA terms in these examples.

As diamonds are created hundreds of miles down into the earth under extreme heat and pressure this can cause marks (think of them as a birthmark). Internal marks are called inclusions and external marks are called blemishes. As with colour, the less natural marks in the stone the more valuable the diamond. The clarity scale goes from Flawless - FL (no internal inclusion or external blemishes) down to Included 3 - I3 (inclusions which are obvious under 10x magnification) Included clarity, imperfections with this reading can quite often been seen with the naked eye.

The majority of diamonds are around VS (Very Slight) to SI (Slightly Included). To grade the clarity of a diamond the size, nature, position, colour and quantity of the marks are all taken into account.

Cut and Proportions of a Diamond

People have often mixed up Cut with the outline Shape of the diamond rather than the arrangement of facets. The Cut of a diamond is all about the proportions and how well made the stone is. The proportions of each facet will affect the stones interaction with light so it's this which gives the diamond it's fire and brilliance (sparkle) along with other factors.

GIA grade the cut from Excellent down to Poor. 

For example if a diamond has been cut too shallow with a rating of poor the stone will appear to have a larger diameter across the top than an excellent cut stone of the same carat weight but the poor cut stone will look flat and will not sparkle as much as the excellent cut diamond as the light can't refract as well.


Polish and Symmetry

Polish and Symmetry are also graded from Excellent down to Poor.

Polish refers to the overall finish (smoothness) of the diamonds surface. These features can be anything from a pit, or a polish scratch to a burn or abrasion, many of which cannot be seen with the naked eye.

Symmetry is as you would expect, how symmetrical each angle line and facet is. Uneven facets or angles can make some diamonds look odd where some which are more subtle you won't be able to tell without inspection with magnification.


This is the visible lights which the stone emits when under an ultraviolet light. The more the diamond glows the stronger the fluorescence. It is measured in strength from Nil up to Extremely Strong

If a diamond has an extremely strong fluorescence the stone may appear hazy/cloudy/oily in natural light. 

Diamond Certificates and Reports

There are many diamond grading laboratories around the world. Different labs have different grading standards, with some labs being a lot more lenient with their standards than others. The GIA, IGI & HRD are the most highly regarded and recognised diamond graders in the world. Therefore when looking for a diamond with a certificate we would only really recommend these three certificates.